1. Field of the Invention
The invention relates to a magnetic transducer, a thin film magnetic head using the same, a method of manufacturing a magnetic transducer and a method of manufacturing a thin film magnetic head. More particularly, the invention relates to a magnetic transducer capable of obtaining the more excellent rate of resistance change, a thin film magnetic head and a method of manufacturing the same.
2. Description of the Related Art
Recently, an improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a hard disk or the like. A composite thin film magnetic head, which has a stacked structure comprising a reproducing head having a magnetoresistive effect (hereinafter referred to as an MR element) that is one of magnetic transducers and a recording head having an inductive-type magnetic transducer, is widely used as the thin film magnetic head.
MR elements include an AMR element using a magnetic film (an AMR film) exhibiting-an anisotropic magnetoresistive effect (an AMR effect), a GMR element using a magnetic film (a GMR film) exhibiting a giant magnetoresistive effect (a GMR effect), and so on.
The reproducing head using the AMR element is called an AMR head, and the reproducing head using the GMR element is called a GMR head. The AMR head is used as the reproducing head whose surface recording density exceeds 1 gigabit per square inch, and the GMR head is used as the reproducing head whose surface recording density exceeds 3 gigabits per square inch.
As the GMR film, a “multilayered type (antiferromagnetic type)” film, an “inductive ferromagnetic type” film, a “granular type” film, a “spin valve type” film and the like are proposed. Of these types of films, the spin valve type GMR film is considered to have a relatively simple structure, to exhibit a great change in resistance even under a low magnetic field and to be suitable for mass production.
FIG. 19 shows the structure of a general spin valve type GMR film (hereinafter referred to as a spin valve film). A surface indicated by reference symbol S in the drawing corresponds to the surface facing a magnetic recording medium. This spin valve film has the stacked structure comprising an underlying layer 91, a soft magnetic layer 92 made of a soft magnetic material, a nonmagnetic layer 94 made of a nonmagnetic material, a ferromagnetic layer 95 made of a ferromagnetic material, an antiferromagnetic layer 96 made of an antiferromagnetic material and a protective layer 97, the layers 92, 94, 95, 96 and 97 being stacked in this order on the underlying layer 91. Exchange coupling occurs on an interface between the ferromagnetic layer 95 and the antiferromagnetic layer 96, and thus the orientation of magnetization Mp of the ferromagnetic layer 95 is fixed in a fixed direction. On the other hand, the orientation of magnetization Mf of the soft magnetic layer 92 is freely changed in accordance with an external magnetic field.
A direct current is fed through the ferromagnetic layer 95, the nonmagnetic layer 94 and the soft magnetic layer 92 in the direction of a biasing magnetic field Hb, for example. However, this current is subjected to the resistance in accordance with a relative angle between the orientation of the magnetization Mf of the soft magnetic layer 92 and the orientation of the magnetization Mp of the ferromagnetic layer 95. Receiving a signal magnetic field causes the change in the orientation of the magnetization Mf of the soft magnetic layer 92 and thus the change in electrical resistance of the spin valve film. This change in the resistance is detected as the change in a voltage. Recently, it has been desired that this rate of resistance change (sometimes referred to as a rate of MR change) be made higher in order to allow magnetic recording at ultra-high density exceeding 20 gigabits per square inch.
A cited reference “CoFe specular spin valves with a nano oxide layer”, 1999 Digests of INTERMAG 99, published by May 18, 1999 reports that the rate of resistance change has been improved by providing an oxide layer called an NOL layer for the ferromagnetic layer of the spin valve film.
However, there is no description about the material and film thickness of the-oxide layer called the NOL layer in the above-mentioned cited reference. Moreover, it is not clear where the NOL layer is formed in the ferromagnetic layer. Furthermore, a relationship between the rate of resistance change and any properties other than the rate of resistance change is not obvious.
More particularly, the above-described known cited reference has a problem that precision of repeatability is deteriorated because a coercive force of the soft magnetic layer is 14 (Oe: oersted), which is greater than 3 (Oe) that is an acceptable limit of the coercive force of a general spin valve film.